PR Review API - Post comment anywhere in changed files

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Summary

The GitHub web UI (new "Files changed" page) allows commenting on any line in a changed file, including unchanged lines outside the diff hunk context. However, the REST API does not support this. Attempting to create a review comment on a line outside the diff hunk context returns a 422 Validation Failed error with "pull_request_review_thread.line" is not part of the diff.

Background

In September 2025, GitHub announced the ability to comment anywhere in a changed file via the new "Files changed" page:

• Blog post: Pull request "Files changed" public preview now supports commenting on unchanged lines (https://github.blog/changelog/2025-09-25-pull-request-files-changed-public-preview-now-supports-commenting-on-unchanged-lines/)
• Feedback discussion: Comment anywhere in a changed file feedback Comment anywhere in a changed file feedback #174786 (https://github.com/orgs/community/discussions/174786)

The announcement explicitly notes:

API support is currently limited, but comments on unchanged lines will be returned by existing APIs and in webhook events.

The Problem

Both the "Create a review comment" (https://docs.github.com/en/rest/pulls/comments#create-a-review-comment-for-a-pull-request) and "Create a review" (https://docs.github.com/en/rest/pulls/reviews#create-a-review-for-a-pull-request) REST API endpoints reject comments targeting lines that fall outside the @@ hunk ranges in the PR diff. The API returns:

422 Validation Failed "pull_request_review_thread.line" is not part of the diff

This is despite:

1. The line parameter being documented as "the line of the blob" (not "the line of the diff")
2. The side parameter supporting RIGHT for "unchanged lines that appear in white and are shown for context"
3. The web UI successfully creating such comments on the same PRs

Existing Community Reports

In the feedback discussion #174786 (https://github.com/orgs/community/discussions/174786#discussioncomment-15410542) (Jan 5, 2026), @928PJY asked about API support for this feature and received no response:

This is the feature we're looking for, but we're posting comments using the API, which currently doesn't support commenting outside the lines around a change. Is this expected? If it's intentional, is there any plan to support this in the future?

Request

Please extend the REST API endpoints for creating review comments (POST /repos/{owner}/{repo}/pulls/{pull_number}/reviews (https://docs.github.com/en/rest/pulls/reviews#create-a-review-for-a-pull-request) and POST /repos/{owner}/{repo}/pulls/{pull_number}/comments (https://docs.github.com/en/rest/pulls/comments#create-a-review-comment-for-a-pull-request)) to accept any valid line number in the file blob for files that are part of the PR diff, matching the behavior already available in the web UI.

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